The present invention relates generally to steam turbine calibration. Specifically, the invention relates to systems and methods of calibrating packing rings which surround turbine shafts.
The present invention is a tool that has been invented in order to reduce the installation time and costs involved in fitting the packing (also called packing ring or labyrinth packing) into a packing holder (also called gland or diaphragm) in the turbine. The packing and packing holder surround, at nominal clearance, the rotor shaft of the turbine. The invention allows expedient and accurate measuring (during installation when the turbine is not operational) of the existing radial, axial and butt gap clearances for each row of labyrinth packing located throughout the turbine.
The majority of steam turbine labyrinth packing, regardless of manufacturer, requires the addition of a spring to be installed behind each packing segment. The packing segments surround the turbine rotor.
Packing segments are usually designed with integral or inserted “teeth”, which can be in-line (same diameter) or hi-low (two diameters) with respect to the turbine rotor.
The purpose of the packing teeth is to create a labyrinth effect or a tortuous path to reduce steam leakage between the stationary packing and the rotating shaft. When teeth are used, grooves are machined in the rotor to accommodate the high-low teeth of the packing.
In order to further minimize shaft leakage, accurate axial alignment is critical. The installation procedure requires close radial and axial clearances to be adhered to in order to avoid tooth rubs during the operation of the turbine.
Under operating conditions, pressurized steam pushes the packing outward away from the packing holder towards the rotor. The steam is not present during downtime. Therefore, the operating conditions must be simulated during installation of the packing. In the past, this has been accomplished with springs or wedges. This has been problematic for several reasons. For instance, wedges are problematic because they are difficult to place and to insure consistent placement for each wedge.
To measure and record the amount of existing radial and axial clearances that exist between the rotor and the packing teeth at installation of the packing, it is necessary to install the packing with the springs behind the segments with the rotor in place. This is a time consuming task, requiring critical man hours to accomplish while the turbine is being reassembled. Any discrepancies found at this time can result in the rotor being removed and a possible delay in the repair time.
The invention consists of a length of flexible pneumatic tubing, sealed on one end, with an air hose connection on the other end, enclosed within a woven fabric sleeve. The tool includes a pneumatic regulator with pressure gauge, and male and female quick disconnect fittings. A male quick disconnect fitting is attached by a hose clamp to the woven fabric sleeve which contains an internal flexible metal strip. The purpose of the strip is to make the hose rigid thereby facilitating insertion into the cavity behind the packing.
The design of the invention embodies a combined system of the described parts to allow expedient and accurate measuring of the radial, axial, and butt gap clearances for each row of packing located throughout the turbine. This invention significantly reduces installation outage time and expense.
With the rotor in place and the packing installed without the springs behind the segments, the invention can easily and quickly be slipped into the packing holder, behind the packing segments. The hose is filled with and expands by pressurized air which immediately raises the packing segments to the close clearance position. Thus, the in operation condition is simulated and accurate measurements can be taken.